I have ridden a Dahon Briza D8 (Dahon Briza D8) and a Castro Duo (Tern folding bike Castro Duo). I have not ridden a Tern Castro D8 (Tern folding bike Castro D 8). You likely need more gearing options than the Castro Duo offers. While the Castro Duo has an adjustable handlepost, the Castro D8 does not. The Briza D8 does have an adjustable handlepost. IMHO, both the Dahon and Tern are excellent bikes. You might want to consider an short vacation in Olney, IL.

-HANK RYAN-
Norman, Oklahoma USA